Igniter for internal combustion engines



Sept. 20, 1938. M. PAULSON 2,130,365

IGNITER FOR INTERNAL COMBUSTION ENGINES Filed June 23, 1936 j :|:':f I

v//W/l// 4G 28" 10" M INVEyTOR WRNE Y Patented Sept. 20, 1938 PATENT OFFICE IGNITER FOR INTERNAL COMBUSTION ENGINES George M. Paulson, New York, N. Y.

Application June 23, 1936, Serial No. 86,729

7 Claims. (Cl. 123--145) This invention relates to electrical incandescent igniters for use in fuel-injection internal combustion engines, especially automotive engines.

Igniters of this class are now used in Dieseltype engines for starting purposes. Their consumption of electrical energy from theA batteries that can be carried on a vehicle has been too great, and their life has been short.

Nevertheless, the utility of this invention is not limited to Diesel engines, since it may be applied to other types of high-compression or supercharged engines. In this connection the invention should provide an effective., durable means for igniting the charges in airplane engines, the development of which is not unlikely to overtax the endurance of jump-spark plugs.

Combustion engine igniters may be grouped in three general classes, as jump-spark plugs, glow plugs and hot bulbs.

Glow plugs is a term applied to resistance element igniters used in Diesel engines to aid in starting. In a Diesel engine the compression ratio is high enough to bring the temperature of the compressed air above the ignition temperature of the injected fuel, so that no igniter is required during normal running, but when the engine is started cold a relatively small glow element will start a flame that propagates through the compressed mixture in the combustion chamber.

The hot bulb class may be considered as including hot bulbs, hot tubes, and'hot plates, of vsuch relatively large mass and surface area as to store heat from one coxbustion stroke to another. In starting and at no load conditions such igniters may be heated by an external flame or electrically.

While various types of glow plugs have been proposed, the kind that has proved to be partially practical for use in starting Diesel engines is one having an exposed resistance element of heavy cross-section made of metal of the highest possible specific electric resistance such as 'chrome-nickel, iron chromium aluminum-cobalt, and like alloys. The known glow plugs which seem to be the more satisfactory are of the order of 2 volt series plugs with very heavy resistance elements. One of these plugs operating on 2- volts draws about 40 amperes, or a consumption of approximately 80 watts for each Plug.

The glow plugs in use, notwithstanding the substantial character of the resistance elements, fail early in service. The failures are due to one or more causes, including breakage from vibration, corrosion under engine combustion conditions, and sagging and shorting of the spiral resistance element causing it to burn out. If it is attempted to operate the plugs at sufliciently high temperature for good and quick starting the life is particularly short. Plugs constructed for 6, 12- orhigher voltages and having longer resistance elements are so weak that the very low voltage plugs are preferred notwithstanding the attendant complication of the wiring system.

The object of this invention is to provide an incandescent igniter which is capable of long' service in an engine, more especially a fuel injection engine, and which can be operated at ,much higher temperatures without likelihood of early failure, thereby aiording sure ignition and quick and sure starting, and which requires only a relatively small part of the electrical energy needed by hitherto existing glow plugs.

These results are secured by employing a resistance element of low specific resistance as compared with chrome-nickel, and by preference one whose resistance increases markedly with increase in temperature, and by so constructing and associating this resistance element and a thin-wall metal case that a compact, short, stout, mechanically strong, composite, incandescent element of high output per unit of surface is Obtained. Plugs of this invention may operate on 12 volts, or as high as the battery voltage may be. The realization of the invention involves the use of a resistance element of filament character, of the approximate order of .005 inch diameter, and the material used both for the filament and for the case is a metal having a high melting point. The case is made of metal having very high resistance to "oxidation or other chemical action. Platinum alloys, such as platinum-iridium or platinum-rhodium, are suitable. The filament may be made of material like that of the case, or may be tungsten or molybdenum if sealed from oxidation. The filament is preferably wound in the form of a helix, which is inserted in the case and insulated therefrom by a thin layer of refractory insulating material. The use of expensive material for the filament and its case does not add materially to the cost of the plug, for the reason that the amounts required by the construction are small, nor is the expense measurable against the effectiveness and length of service.

The wall thickness of the case is substantially no lgreater than necessary to obtain the requisite mechanical strength. This and the thlnness of between the tapered portions the insulation separating the filament from the case result in small temperature gradient between the filament and the outside surface of the case. Another feature of the construction which ,enables the invention to obtain temperatures on the outside of the case which are close to the filament temperature, and to maintain such temperatures without excessive input of electrical energy, is that the case conforms closely to the filament so that the radiating surface is small. The saving which this effects in electrical energy is important since radiation is proportional to the fourth power of the absolute temperature of the surface. Another effect of the thinness of the case is that it reduces loss of heat by conduction to the body of the plug, and thus reduces the amount of electrical energy required to maintain the high temperature on the surface of the incandescent element.

By still another feature of the invention heat conduction loss may be greatly reduced, with important increase in the efficiency of the composite heating element. To this end a section or sections of relatively low thermal conductivity are interposed between the incandescent part of the filament case and the rplug body.

The igniters of this invention are adapted for operation with impunity and economy at excep' tionally high surface temperatures with a power input of the order of 33 Watts.

In the accompanying drawing, forming part hereof:

Fig. 1 is a side View, mostly in section, showing an incandescent igniter made in accordance with this invention;

Fig. 2 is an enlarged side view of one portion of the igniter shown in Fig. 1, with the incandescent element shown in section;

Fig. 3 is a view similar to Fig. 2, but on a reduced scale and partly broken away, showing a modified form of the invention;

Fig. 4 is an end view of the modified form of the invention shown in Fig. 3; and

Fig. 5 is a view similar to Fig. 3 showing a second modified form of the invention.

The igniter shown in Figs. 1 and 2 includes a body portion I connected to one end of a sleeve II which has threads along a part of its outside surface for screwing of the igniter into an opening in the wall of an engine cylinder. The sleeve II has a hexagonal fiange I2 to which a wrench can be applied. 'I'he body portion I0 extends into a recess in the end of the sleeve II and is held firmly in this recess by brazing or by crimping the end of the sleeve.

The bore of the sleeve I I is tapered for most of its length to receive a spindle I5. The spindle has a tapered portion which is wedged into the sleeve II with mica insulation I6 compressed of the spindle and the sleeve bore. The spindle I is held in place by a nut I'I threaded over the outer end of the spindle. This nut is electrically insulated from th-e end of the sleeve II by mica washers I9.

A composite incandescent element 2| is connected to the body portion I0. This incandescent element includes a metal filament 22 having a high melting point. 'I'he filament 22 is preferably a platinum alloy, such as platinumiridium or platinum-rhodium, which does not oxidize at high temperatures. Metals such as tungsten or molybdenum are suitable if sealed from the atmosphere. The small diameter of the filament gives it limited surface area, which resuits lin intense heating for a given electrical input.

The filament is wound in a helix and enclosed in a tubular case 24. This case is a U-tube and has end portions 25 of metal having a lower thermal conductivity than the middle part of the U-tube. The end portions 25 are welded or brazed to the other part of the U-tube and their purpose is to reduce the flow of heat from the U-tube to the body portion I0 into which the end portions 25 extend and to which they are secured by brazing or welding. Most of the convolutions of the lament are in the curved part of the U-tube where the heating of the incandescent element is concentrated.

The case 24 closely surrounds the coil, the inside diameter of the case being only slightly greater than the outside diameter of the filament helix. This keeps the radiating surface of the incandescent element small and makes it possible to maintain the surface at a high temperature with the expenditure of a relatively small quantity of electrical energy. The inside of the case 24 is filled with refractory insulating material 26, to keep the convolutions of the filament apart and to prevent contact of the filament with the case.

The wall of the case is virtually no thicker than is necessary to obtain the desired mechanical strength for the incandescent element. The thinness of the insulation 'combined with the thinness of the case results in a small Itemperature gradient between the filament and the outside surface of the case so that the surface temperature of the incandescent element is not far below the filament temperature.

One end of the filament 22 is electrically connected with the spindle I5 by a leader wire 28 and a spindle coil 29. The leader wire 28 is preferably welded to the filament 22 ard coil 29. The leader wire 28 passes through the body portion I0 and is surrounded by insulation 30, which is preferably ceramic. The other end of the filament is grounded by a connection 3I to the case or to the body portion of the igniter.

By using a filament material whose resistance increases markedly with increase in temperature, the filament is protected from overheating since heating of the incandescent element by the combustion in the cylinder increases the resistance of the filament, decreases the current fiowing,

and thereby reduces the electrical heating of the filament.

Striking performance may be obtained with a platinum-indium filament of .0055 inch diameter, and a case of the same material made from .072 inch tubing having a wall thickness of .005 inch.

The insulation 26 is preferably powdered quartz, which becomes fused, though other materials such as magnesium oxide or aluminum oxide are suitable. A thickness of insulation of .010 inch between the filament and the wall of the case is sufiicient. The incandescent element 2| may be bent into a U-tube having an outside radius of .1775 inch for the curved part of the U, with straight sections of .20 inch for the straight portions of the U. Specific dimensions given herein are illustrations of an order of magnitude.

Figs, 3 and 4 show a modified form of the invention in which an incandescent element 32 comprising two straight tubes 33 joined by a bridge 34 takes the place of the U-tube incandescent element 2I. There is a filament 35 in each of the tubes 33, and these filaments are coiled and covered with insulation 25. 'Ihe two filaments 35 are connected in parallel in Fig. 3, and each filament has a separate leader wire 28' extending through the body portion IIIIl and connected with the spindle coil 29. 'Ihe ends of the filaments 35 remote from the leader wires 2li are connected to the bridge 34 and the return circuit back to the body portion of the igniter is thus made to include the straight tubes 33 which are the cases for the filaments 35. Each of the tubes 33 preferably has an end portion 35 of lower thermal conductivity than the portion around the filament coil. These end portions reduce conduction losses from the tubes 33 to the body portion of the plug.

Fig. shows a second modified form of the invvention having a centrally located incandescent element 42 comprising a single straight tubular case 43 enclosing a coiled filament 45 surrounded by insulation 26. The case 43 is a part of the electric circuit, as in Fig. 3, but the filament 45 is of lower resistance than either of the filaments 35 because it must carry all of the heating current whereas each of the coils in Fig. 3 carries only one-half of the current. The leader wire 28b extends through a central opening in the body portion b and is connected with the spindle coil 29". An end portion 45 of lower thermal conductivity than the portion of the case around the filament coil joins the case to the body portion il!b but reduces conduction losses from the case to the body portion of the plug.

Still other modifications of the invention may be devised.

I claim:

l. An ignition device for internal combustion engines, including an incandescent element comprising a thin metallic filament of high melting point and high resistance to oxidation enclosed Within and closely conforming at substantially all points along its length to a thin-wall protecting case of metal having high melting point and high resistance to oxidation, the wall thickness of the case being only sufficient to give required mechanical strength to withstand working conditions, and electrical insulation between the filament element and the wall of the case.

2. An electrical incandescent igniter comprising a metal high melting filament having a diameter of the order of .005 inch, a thin-wall case of metal having high melting point and high resistance to oxidation, enclosing the filament, said lament conforming closely to the case at substantially all points along the length of the filament, and insulating material of slight thickness between the filament and the case.

3. An igniter for internal combustion engines, including in combination a coiled, thin, metal filament of high melting point, insulating material thinly surrounding the nlament coil, and a platinum-alloy case surrounding and supporting the coiled lament and comprising the incandescent surface of the igniter, said case having a wall of the orderof thinness of the filament, and said filament conforming closely to the case at substantially all points along the length of the nlament.

4. In an igniter for internal combustion engines, a composite incandescent element comprising a thin-wall U-tube with its ends connected to the body portion of the igniter, and a filament of high melting point closely surrounded by the tube and coiled in the curved portion of the tube to obtain a substantial length of the filament in that portion of the tube, said tube being of a. high melting point metal which resists oxidation at the cylinder temperatures ofan internal combustion engine.

5. In an electrical incandescent igniter, a coiled filament enclosed in a thin-walled metal case having a high melting point and high resistance to corrosion, means supporting the case, and one 0r more heat flow obstructions connecting the case with the supporting means.

6. In ignition device including a body portion and a. composite incandescent element connected to and supported by the body portion, said element comprising a coiled metal filament of high electrical resistance and high melting point, insulation surrounding the filament, and a thinwall metal case enclosing the filament and having end sections of relatively low thermal conductivity for impeding the flow of heat from the case to the body portion.

'7. An incandescent igniter for internal cornbustion engines comprising a body portion, a coil of thin metallic filament of high melting point and high resistance to oxidation, means supporting the filament coil from the body portion, the supporting means comprising a metal case made of metal having a high melting point and high resistance to oxidation and surrounding the lament coil, said filament conforming closely to the case at substantially all points along the length of the filament, and said case having a wall with substantially only enough thickness to supply the mechanical strength to support and protect the lament coil under the Working conditions of the engine, and insulating material between the coil and the wall of the case and between and within the convolutions of the filament.

GEORGE M. PAULSON. 

